Integrator circuits of the type described herein are for instance used for forming pulses. They enable rising and dropping portions of predetermined slopes to be generated, with a zone of constant voltage defined by the limitation arranged therebetween.
There exist essentially two different ways of obtaining such limitation. In the case of the active limitation, a control circuit is activated to maintain the voltage at the capacitor constant, when the limit voltage has been reached. For this purpose, the amplification of the control circuit must be kept low to allow rapid transient of the control circuit. However, this means that the limiting voltage does not remain constant and that the difference between the start and the final value of the limitation is relatively high.
In the case of the passive limitation, a clamping circuit with diodes is used which receives the constant current previously supplied to the capacitor after the clamping voltage has been reached. However, the particular current/voltage characteristic of the diodes results in a voltage discontinuity during the transition from the constant clamping voltage to the dropping slope (discharge of the capacitor), and as a result thereof the pulse shape becomes inaccurate. Although this voltage discontinuity can be avoided by passing the pulse through an additional limiter circuit which clips off the inaccurate portion of the pulse, such procedure offers the disadvantage that the contant-voltage time varies with any change of the slope of the rising and/or dropping portion. However, in many applications, it is desired that this contant-voltage section should remain uniformly long even if the slope should be varied.